Multiplex radio system



Patented duly l5, 1924.

LLOYD Esrnnscninn, or -HOLLIS,'NEW Yo RK, assreivon TO AMERICAN 'rnLnriion-n AND TELEGRAPH .COMPANY',A GOEPORATIONOF NEW YORK.

Mutter-FLEX name SYSTEM.

Application filed September 26, 1919.

fication.

This invention relates to radio systems and more particularly to arrangements for multiplex signaling by .means of radio systems.

.Qnc of the principal features of the 1- nvention resldes in the provision of oppositedirected channels for associating different low frequency signaling circuits with a common antenna system.

Another feature of the lIlVGIltlOD. resides in the provision of multiple balancing arrangements combined with selective devices, for separating the channels of different circuits and for separating the east and west bound channels, .of the same circuit in a system such as just described.

A still further feature of the invention residrs in the association of each .o'fia plurality of :low frequency signaling circuits with a common antenna arrangement by means of a circuit organization similar to that of the so-called 22 type of repeater circuit, so that automatic repeating is effect-ed between each low frequency signaling circuit of the multiplex system and the radio system proper.

A still further feature of the invention resides in the use of separate sending and receiving antenna for a multiplex radio system, together with means for balancing the effect of the sending antenna upon the receiving antenna, said means being operative for a plurality of signaling channels.

The embodiment of these features, together with other features of the invention more fully hereinafter appearing, may be understood from the following description when read in connection with the accompanying drawings, Figures 1 and 20f which constitute simplified circuit diagrams illustrating two forms of the invention, while Figures 3 and 4 illustrate details of theap- E2, including the usual-tuning inductance 3.

L and L designate low frequency signaling circuits which may be ordinary tele Serial No. 326,522.

.phone transmission lines. The lines L and i i are connected with the common high frequency transmitting bus bars TL, through transmitting channels TL and TL and are similarly associated with the high frequency receiving bus bars 'R-L through receiving chanels EL, and RL In order to render the corresponding .transmitting and receiving channels associated with each low frequency circuit substantially conjugate with respect to eachother, the low frequencylines L and L are balanced by artificial lines or networks N and N The antenna A is balanced by means of a network AN, for the purpose of rend-en ing the bus circuits TL and RL substantial- .ly conjugate with respect to each other at radio frequencies. The bus circuit BL is associated withthe antenna by means of a balanced transformer arrangement 4:, While a connection 5 extends from the .midpoint of the antenna winding of the transformer 4 to one of the bus bars, TL, the-other bus bar being connected to ground, as shown. It will thus be seen .tliateach of the lines such as L L is associated With the com .mon antenna through an organizationsomewhat similar to that of-the so-called 22 repeater circuit.

In order to translate the loW frequency signals from the line L into high he quency radio frequencies, a modulator 1M, is included in the transmittingchannel TL This modulator may-be of any WGlldHlOWIl type is illustrated in simplified form in Figure 3 and comprises a pair of three-element vacuum tubes 6 and 7, connected in a balanced circuit in such a manner that carrier frequencies applied to the tubes over the circuit 8 will produceno effect upon fthe outgoing circuit 9, unless signaling nequencies are applied to the incoming circuit 10. When ;low frequency signaling currents are applied to the incoming circuit 10, however, modulated carrier currents are i impressed upon the circuit 9, having an amplitude directly proportional to that .of the low frequency signaling currents.

The transmitting channel TL is also projvided with an amplifier TA which may be .140

' of high frequencies.

of any well-known type, but is preferably an amplifier of the vacuum tube type. if desired, this amplifier may be constructed to operate as a. push and pull amplifier, such as illustrated in Figure 4, an amplifier of this type having the advantage that it produces a minimum amount ofdistortion As amplifiers of this character are well-known no detailed description thereof is necessary.

A filter TF may be included in the channel TL between the modulator M, and the amplifier TA This filter is preferably of the type disclosed in the U. S. patents issued to George A. Campbell, Nos. 1,227 ,113 and 1,227,114, dated May 22, 1917. This filter may be of the high pass type and should be so constructed as to freely transmit a band of frequencies extending above the frequencies employed in ordinary signaling, while suppressing low frequencies. A second filter TF may be included between the amplifier TA and the bus bars TL. This filter is also of the type disclosed in the Campbell patents above referred to and? should be designed to transmit a band of frequencies in the neighborhood of the carrier frequency assigned to the channel, the Width of the bandbeing sufiicient to accommodate the range of frequency variation due to the modulation of the carrier frequency by low frequency signals.

The receiving channel BL, is provided with a demodulator or detector D, for the purpose of translating the radio frequencies into low frequency signals. This detector may be ofany well-known type, but is preferably a duplex balanced vacuum tube detector of the type disclosed in the U. S. patent to John R. Carson, No. 1,348,308, issued June 15, 1920. As described in said application of John R. Carson, this type of detector may be identical in construction with the duplex modulator already referred to and the diagram of .Figure 3 applies equally well to both the modulator and demodulator. The demodulator operates upon the socalledhomodyne principle and is therefore supplied with carrier currents of the frequency assigned to" the receiving channel, over the circuit 8, while the modulated carrier currents to be detected are applied over the circuit 10 and the resultant low frequency currents appear in the outgoing circuit 9.

Owing to the enormous difference in the 'magnitude of the transmitted energy, as

compared with the received energy in a Wireless system, it is desirable that the separation due to balance between oppositely directed channels be supplemented by frequency separation; accordingly if a frequency f, is assigned to the transmitting channel TL a different frequency f, will be assigned to the receiving channel BL and tivity, the receiving channel RL may be provided with a filter R11, which is in general similar to the filter TF except that it transmits a band of frequencies in the neighborhood of the frequency f,, instead of a band in the neighborhood of the frequency f,.

If, however, both the transmitting and receiving channel have the same frequency assigned thereto, filter RF will be identical in construction with filter TF In order to amplify the low frequency currents detected by the demodulator 1),, an amplifier BA, is provided. This amplifier may be of the push and pull type illustrated in Figure l, but since the amplifier only amplifies low frequency currents, it is usually suflicient to provide a simple vacuum tube amplifier of ordinary construction. In addition to the amplifier HA the receiving channel BL, also includes a filter RF This filter is also of the general type disclosed in the patents to Campbell, above mentioned, and is designed to transmit the low frequency detected signals, while suppressing higher frequencies.

Similarly the transmitting channel TL is provided with a modulator M a filter TF identical in construction with the filter TF and amplifier TA identical in construction with the amplifier TA,, and a band filter TF The latter filter is similar to the filter TF but transmits a band of frequencies in the neighborhood of the carrier frequency f assigned to this channel, which frequency should be substantially different from either frequency f, or 7",. So also the receiving channel RL is provided with a filter RF identical in construction with the filter RF an amplifier RA identical in construction with the amplifier HA a demodulator D and a filter RF The demodulator D is similar to the demodulator D already described, but is supplied with a different carrier frequency 7 The filter RF is in general similar to the filter RF but transmits a band of frequencies in the neighborhood of the carrier frequency f,, instead of in the neighborhood of the frequency f,.

The operation is as follows:

Low frequency signals incoming from the line L are transmitted through the transformer 11 to the channel TL and impressed upon the modulator M thereby modulating carrier frequency f,, so that the modulated high frequency currents are passed through the filter TF and amplified by the amplifier TA The amplified currents are then passed through the filter TF to the bus bars TL. At the same time other modulated high frequency currents from other transmitting channels are also impressed upon the bus bars and all of the modulated currents are then transmitted over conductor to the midpoint of the antenna winding of the transformer 4. Halfof the energy is thereing only that due t'ounbalance. Theenergy thus transmitted to the receiving bus bars RL may be substantially prevented from reacting upon the receiving channels "BL, and 1H),, by reason of the fact that these receiving channels have assigned to them frequencies differing substantially from the transmitting frequencies and hence the transmitting energy reacting upon the bus bars BL is substantially suppressed by the filters RF, and RF Modulated high frequency currents transmitted from the antenna of a distant station are absorbed by the antenna A and are impressed through the transformer 4 upon the receiving busbars FL. The frequencies corresponding. to the several receivingchannels are separated and selected into the proper channels by the filters RF, and-RF and are then impressed upon the demodulators D and D The demodulator-s operate to detect the low frequency signaling currents in accordance with whichthe high frequency currents are modulated and the detectedcurrents, after being amplified by the ampli fiers RA, and RA the low frequency currents are passed through the :low passfilters RF and RF to the signaling lines L and L Instead of using a single antenna both for transmitting andreceiving, separate antennae may be used, as indicated in Figure 2. In this figure AT designates a transmitting antenna having an aerial 21 and a vertical member 22 including the usual tuning inductance 25. AR designates a receiving antenna having an aerial 24 and a vertical 25, including a tuning inductance 26. The transmitting bus bars TL are connected to the transmitting antenna AT through a transformer 27, while the receiving busbars RL are similarly connected to the receiving antenna AR through a transformer 28. In practice it is desirable to locate the transmitting and receiving antenna some distance apart and where this is done the receiving bus bars BL may be connected to the transformer 28 through a section of transmission line B L. Theassociation of signaling lines L and L, with the transmitting and receiving bus bars will be the same as in Figure 1 and need not be further described.

It will be apparent that a certain amount of transmitting energy radiated by theantenna AT will be received by the antenna and transferred over the line BL to the'receiv-ing bus bars RL. In order to balance out this energy, a balancing line BL is arranged to interconnect the antennae AT and AB through loose-coupling transformers 29 and 30. This balancing circuit may be of any suitable character, but is illustrated as a full metallic line, including an adjustable network BN for adjusting the transmission eliiciency of the line and the phase angle of the current. The balancing line BL may also include an amplifier BA for further determining the amplitude of the currents transmitted over the line. This amplifier may be of any well-known type, but is preferably a vacuum tube amplifier. \Vhere a fullmetallic circuitis used it should preferably be transposed, as indicated, to prevent imbalances to ground with respect to the exposure of the sending antenna, in order to avoid the production of currents of different phases .in the line BL. By a proper adjustment of the various elements of the line BL, energy may be impressed upon the receiving antenna AR over said line, said energy being substantially equal to that absorbed by the antenna Aft from the transmitting antenna AT and having anopposite phase relation with respect thereto, so that only'the relatively small amount of energy due to unavoidable unbalance will be transferred :over the circuit RL to the receivingabusbars RL. This relatively small amount of energy may be prevented from reacting upon the receiving channels by the action of the filters RF, and RF as described in connection with, Figure 1. it will be understood that this is but one specific means for effecting high frequency balance between separate sending and receiving antenna, and that other eXped-ients may be used such as "that of a loop receiving antenna disposed to be non-receptive from the home transmitting antenna.

The operation of Figure 2 is as follows:

The low frequency signals incoming from the lines L and L after being translated into high frequency currents by the apparatus associated with the transmitting channels TL and TL in the manner described in connection with Figure 1 are impressed uponthe transmitting bus bar'TL and transmitted through the transformer 27 to the sendingant'enna AT. The energy impressed upon this antenna is radiated to the distant station, a certain amount of the energy, however, being absorbed by the receiving antenna AR. At the same time, however, an

equal amount of energy istransferred over the balancing line BL, and impressed upon the receiving antenna AR through the transformer 30, so that the absorbed energy is substantially neutralized and only arelatively small amount of energy due to unbalance reacts upon the receiving bus bars, BL. High frequency currents radiated from a distant sending station are absorbed by the receiving antenna 24 and impressed through the transformer 28 upon the connecting circuit BL leading to the receiving bus bars R-L. The filters RF and RF, operate to select into the proper receiving channels the several received frequencies which are translated into low frequency sig naling currents and impressed upon the signaling linesL and L in the manner already described in connection with Figure 1.

It will be understood that while but two signaling circuits are shown associated with the antenna arrangements of Fignresl and 2, in practice a larger number of signaling circuits may be associated with the antenna by'connecting the transmitting and receiving channels thereof to the transmitting and receiving bus bars.

It will furthermore be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

'1. In a radio system, an antenna arrangement, a plurality of paths for superposing different transmitting frequencies upon said antenna arrangement, selective devices in each of said paths for maintaining frequency separation therebetween, a plurality of paths upon which different receiving frequencies may be impressed from said antenna arrangement, selective devices in each of said last mentioned paths for selecting to each path its proper frequency, means for balancing said antenna arrangement, whereby all of said transmitting paths may be maintained substantially conjugate with respect to all of said receiving paths, a plurality of signalling circuits, and means for associating each signalling circuit with a transmitting path and corresponding receiving path.

2. In a radio system, an antenna arrangement comprising a transmitting antenna and a receiving antenna, a plurality of paths for transmitting difi'erent signaling frequencies to said transmitting antenna, selective devices in said paths for maintaining frequency separation therebetween, a plurality of paths for receivingdifl'erent frequencies from said receiving antenna, selective devices associated with said last mentioned paths for selecting the proper frequencies to each path, means associated with said antenna arrangement for rendering all of said transmitting paths substantially conjugate at radio frequencies with respect to said receiving paths, a plurality of signalling circuits, and means for associating each signalling circuit with a transmitting path and corresponding receiving path.

3. In a radio system, an antenna arrangement comprising a transmitting antenna and a receiving antenna, a plurality of paths for transmitting different signaling frequencies to said transmitting antenna, selective devices in said paths for maintaining frequency separation therebetween, a plurality of paths for receiving different frequencies from said receiving antenna, selective devices associated with said last mentioned paths for selecting the proper frequencies to each path, means associated with said antenna arrangement for rendering all of said transmitting paths substantially conjugate with respect to said receiving paths, said means comprising a circuit for trans mitting energy from said transmitting antenna to said receiving antenna, to balance the energy radiated from said transmitting antenna to said receiving antenna, a plurality of signalling circuits, and means for associating each signalling circuit with a transmitting path and corresponding receiving path.

a. In radio system, an antenna arrangement, a plurality of low frequency signaling circuits, a transmitting path associated with each circuit for translating low frequency signals incoming from the circuit into radio frequencies for radiation by said antenna arrangement, a receiving path associated with each signaling circuit, for translating radio frequencies received from said an tenna arrangement into low frequency signals for transmission over said signaling circuits, means to balance each signaling circuit, thereby rendering the associated transmitting and receiving paths substantially conjugate with respect to each other at low frequencies, and means associated with said antenna arrangement and common to all of said paths for rendering all of the transmitting paths substantially conjugate with respect to the receiving paths at radio frequencies.

In testimony whereof I have signed my name to this specification this 25th day of September, 1919.

LLOYD ESPENSCHIED 

